Method for recovering Mn and Zn from dust of bag-type dust collector after thermal desorption of soil
By separating and recovering Mn and Zn through magnetic attraction and chemical reaction, the environmental impact of dust disposal after thermal desorption has been solved, and efficient heavy metal recovery and resource utilization have been achieved.
Patent Information
- Application Number
- CN202511633174.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-10
- Publication Date
- 2026-01-30
AI Technical Summary
In existing technologies, the method of mixing dust generated after thermal desorption with soil for disposal can easily affect environmental quality, especially the migration of heavy metals, which affects groundwater and land development, and there is a lack of high-value resource utilization pathways.
Ni and Fe in dust are removed by magnetic attraction. The reaction is carried out with alkaline solution under alkaline conditions by adjusting the pH value, and then with acid solution under acidic conditions to separate and recover Mn and Zn. The separation and recovery of heavy metals are achieved by using magnetic attraction and chemical reaction.
It achieves efficient recovery of Mn and Zn, reduces environmental impact, provides a high-value resource utilization pathway for dust, and improves the recovery rate of heavy metals.
Smart Images
Figure CN121428299A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of resource recycling technology, specifically relating to a method for recovering Mn and Zn from dust in a baghouse dust collector after soil thermal desorption. Background Technology
[0002] Currently, thermal desorption technology for treating contaminated soil is developing rapidly. Thermal desorption can efficiently treat various hydrocarbon pollutants, but it generates a significant amount of solid matter after desorption. In addition to the desorbed soil produced at the rotary kiln outlet, the solid waste generated by the direct-fired thermal desorption process also produces dust, which is collected in a baghouse dust collector. Figure 1 As shown.
[0003] Regarding the issue of large amounts of dust generated by direct-fired thermal desorption technology, the current conventional approach is to mix the dust collected in the direct-fired thermal desorption bag filter with the soil after thermal desorption and then dispose of it centrally. Figure 2 As shown. However, regardless of whether the dust is disposed of in a landfill or after mixing, the concentration of heavy metals in the dust must be monitored, especially heavy metals with a high proportion of migratory components. When the concentration of heavy metals in the dust mixed with the treated soil reaches a certain level, the migration of heavy metals will affect the environmental quality of groundwater, thereby affecting the development and reuse of the site and surrounding land. Therefore, it is urgent to develop a resource utilization pathway and method for dust collected by bag filters to achieve high-value resource utilization of dust, while reducing the environmental impact of common dust treatment and disposal methods. Summary of the Invention
[0004] In view of this, the object of the present invention is to provide a method for recovering Mn and Zn from dust in a baghouse dust collector after soil thermal desorption. The method provided by the present invention can effectively recover Mn and Zn, realize waste reuse, and eliminate the potential environmental impacts that may exist with current dust disposal methods.
[0005] This invention provides a method for recovering Mn and Zn from dust in a baghouse dust collector after soil thermal desorption, comprising the following steps: Ni and / or Fe in dust are removed by magnetic attraction to obtain magnetically attracted dust. The magnetically attracted dust and alkaline solution are mixed for a first reaction, followed by a first solid-liquid separation to obtain a solid after alkaline washing; the pH value of the alkaline solution is 12-14. The solid after alkali washing and the acid solution are mixed for a second reaction, followed by a second solid-liquid separation to obtain a solution containing Mn and Zn; the pH value of the system after mixing the solid after alkali washing and the acid solution is 4.5~6.5.
[0006] Preferably, the pH value of the alkaline solution is 12.5 to 13.5.
[0007] Preferably, the alkaline solution comprises a hydroxide solution.
[0008] Preferably, the ratio of the amount of dust and alkaline solution used after magnetic attraction is 1g:5~20mL.
[0009] Preferably, the first reaction is carried out under oscillation conditions, wherein the oscillation rate is 10~200 rpm and the time is 12~36 h.
[0010] Preferably, the pH value of the mixture of the solid and acid after alkali washing is 5-6.
[0011] Preferably, the ratio of the solid to the acid solution after alkali washing is 1g:5~20mL.
[0012] Preferably, the second reaction is carried out under oscillation conditions, wherein the oscillation rate is 10-200 rpm and the time is 12-36 h.
[0013] Preferably, the dust is ball-milled and sieved before processing, and the undersize portion is collected; the sieve mesh size is 150 mesh.
[0014] Preferably, the magnetic attraction method is a two-stage electromagnetic separation, wherein the first stage magnetic induction intensity of the two-stage electromagnetic separation is 0.5~0.7T and the second stage magnetic induction intensity is 1.2~1.8T.
[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for recovering Mn and Zn from dust in a baghouse dust collector after soil thermal desorption, comprising the following steps: removing Ni and Fe from the dust using a magnetic adsorption method to obtain magnetically adsorbed dust; mixing the magnetically adsorbed dust with an alkaline solution to carry out a first reaction, followed by a first solid-liquid separation to obtain an alkaline-washed solid; the pH value of the alkaline solution is 12-14; mixing the alkaline-washed solid with an acid solution to carry out a second reaction, followed by a second solid-liquid separation to obtain a solution containing Mn and Zn; the pH value of the system after mixing the alkaline-washed solid and the acid solution is 4.5-6.5.
[0016] Based on the leaching characteristics of heavy metals in dust, this invention achieves the recovery of heavy metals Mn and Zn from dust by adjusting the pH value. The operation is simple and the recovery rate of Mn and Zn is high. At the same time, it solves the problem that current dust disposal methods are prone to affecting the surrounding environment. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 A schematic diagram of the process for generating solid substances in an ex-situ direct-fired thermal desorption process; Figure 2 A schematic diagram of the mixing and disposal of solids generated by ex-situ direct-fired thermal desorption. Figure 3 This is a flowchart of the method for recovering Mn and Zn from dust in a baghouse dust collector after thermal desorption of soil according to the present invention; Figure 4 This is a graph showing the change of As ion concentration with solution pH in the experimental examples of this invention; Figure 5 This is a graph showing the change of Cr ion concentration with solution pH in the experimental examples of this invention; Figure 6 This is a graph showing the change of Zn ion concentration with solution pH in the experimental examples of this invention. Detailed Implementation
[0019] This invention provides a method for recovering Mn and Zn from dust in a baghouse dust collector after soil thermal desorption, comprising the following steps: Ni and / or Fe in dust are removed by magnetic attraction to obtain magnetically attracted dust. The magnetically attracted dust and alkaline solution are mixed for a first reaction, followed by a first solid-liquid separation to obtain a solid after alkaline washing; the pH value of the alkaline solution is 12-14. The solid after alkali washing and the acid solution are mixed for a second reaction, followed by a second solid-liquid separation to obtain a solution containing Mn and Zn; the pH value of the system after mixing the solid after alkali washing and the acid solution is 4.5~6.5.
[0020] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.
[0021] This invention uses a magnetic attraction method to remove Ni and / or Fe from dust, resulting in magnetically attracted dust.
[0022] In this invention, the soil thermal desorption is preferably soil ex-situ direct combustion thermal desorption, and the dust is collected in a bag filter after thermal desorption.
[0023] In this invention, the dust is preferably ball-milled and sieved before use, and the undersize portion is taken; the mesh size of the sieve is preferably 150 mesh.
[0024] This invention does not impose any special requirements on the magnetic attraction method. Specifically, a two-stage electromagnetic separation can be employed. The first-stage magnetic induction intensity of the two-stage electromagnetic separation is preferably 0.5~0.7T, specifically 0.6T, and the second-stage magnetic induction intensity is preferably 1.2~1.8T, specifically 1.5T. The magnetic attraction method of this invention has a high removal rate of Ni and Fe from dust, and can also remove some Cr.
[0025] After obtaining the magnetically attracted dust, the present invention mixes the magnetically attracted dust with alkaline solution to carry out a first reaction and a first solid-liquid separation to obtain an alkaline washed solid (i.e., the magnetically attracted dust is alkaline washed with alkaline solution).
[0026] In this invention, the pH value of the alkaline solution is preferably 12.5 to 13.5, specifically 13; the alkaline solution preferably includes a hydroxide solution, and the hydroxide solution is preferably a sodium hydroxide solution.
[0027] In this invention, the preferred ratio of the amount of magnetically attracted dust to the amount of alkaline solution is 1g:5~20mL, specifically 1g:10mL.
[0028] In this invention, the first reaction is preferably carried out under oscillation conditions, with the oscillation rate preferably being 10-200 rpm, specifically 30 rpm, and the time preferably being 12-36 h, specifically 24 h. During the first reaction, As and Cr dissolve in an alkaline solution within a specific pH range, while Mn and Zn remain insoluble, thus achieving the purpose of removing As and Cr from the dust. Under alkaline conditions, the DOM (dissolved organic matter) in the soil colloids contained in the dust can form stable complexes with heavy metals, dissolving in the aqueous solution; As and Cr ions bind to smaller colloidal molecules or DOM particles and remain in the solution; within the pH range of 8-13, the number of As ions in the solution increases with increasing pH.
[0029] In this invention, the first solid-liquid separation is preferably centrifugation and / or filtration. In specific embodiments, centrifugation is performed followed by filtration. The pore size of the filter membrane is preferably 0.45 μm, 0.22 μm, 100 kDa, or 10 kDa. As the pore size of the filter membrane gradually decreases from 0.45 μm to 10 kDa, the amount of heavy metal ions in the filtrate gradually decreases. Under alkaline conditions, more DOM molecules dissolve, resulting in a higher concentration of macromolecules in the leachate system, smaller pore sizes, and a slower filtration rate.
[0030] After obtaining the alkali-washed solid, the present invention mixes the alkali-washed solid with acid solution to carry out a second reaction, and then separates the solid and liquid to obtain a solution containing Mn and Zn (i.e., acid washing the alkali-washed solid with acid solution).
[0031] In this invention, the pH value of the system after mixing the solid and acid solution following alkaline washing is preferably 5-6, specifically 5.5. The acid solution is preferably a nitric acid solution.
[0032] In this invention, the preferred ratio of the solid to the acid solution after alkali washing is 1g:5~20mL, specifically 1g:10mL or 1g:20mL. Under acidic conditions, Mn and Zn dissolve in the solution.
[0033] In this invention, the second reaction is preferably carried out under oscillation conditions, wherein the oscillation rate is preferably 10-200 rpm, specifically 30 rpm, and the time is preferably 12-36 h, specifically 24 h. During the second reaction, Mn and Zn dissolve in an acidic solution within a specific pH range, while other metal ions do not dissolve or dissolve only slightly. Subsequent solid-liquid separation yields a solution containing Mn and Zn, thereby removing other metal ions and solid substances.
[0034] In this invention, the second solid-liquid separation is preferably centrifugation and / or filtration. In the embodiments of this invention, centrifugation is performed first, followed by filtration. The pore size of the filter membrane is preferably 0.45 μm, 0.22 μm, 100 kDa, or 10 kDa.
[0035] In this invention, after obtaining the solution containing Mn and Zn, it is preferable to further include: recycling the solution containing Mn and Zn; this invention does not have special requirements for the recycling method, and methods commonly used by those skilled in the art can be adopted, specifically for preparing Mn-Zn alloys or Mn-Zn ferrites. The Mn-Zn alloys can be used in the electronics and automotive fields.
[0036] To further illustrate the present invention, the method for recovering Mn and Zn from dust in a baghouse dust collector after soil thermal desorption, provided by the present invention, will be described in detail below with reference to the accompanying drawings and embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.
[0037] In the embodiments and comparative examples of this invention, the heavy metal content in the dust (raw ash) of the bag filter after soil thermal desorption is shown in Table 1.
[0038] Table 1. Concentration of heavy metals in raw ash (unit: mg / kg)
[0039] In this embodiment of the invention, the main reagents prepared are as follows (dilute as needed before use): (1) Nitric acid solution (2.0 mol / L): Take 138.89 mL of concentrated nitric acid (65wt%) and dilute to 1 L with ultrapure water; (2) Sodium hydroxide solution (1.0 mol / L): Weigh 40 g of analytical grade sodium hydroxide, dissolve it, and dilute to volume in a 1 L volumetric flask and mix well.
[0040] Experimental Example 1g of dust was mixed with 5 mL of acidic or alkaline solutions with pH values of 2, 4, 5.5, 7, 8, 9, 10.5, 12, and 13, respectively. The mixture was shaken at 30 rpm for 24 h. After shaking, the mixture was centrifuged to obtain the supernatant, which was then filtered through a 0.45 μm filter membrane. The concentrations of As, Cr, and Zn ions in the solution were then determined.
[0041] The results are as follows Figures 4-6 As shown, it can be seen that under alkaline conditions, the concentrations of As and Cr ions increase with increasing pH value, while the leaching concentration of Zn ions is higher under acidic conditions.
[0042] In the following embodiments, according to Figure 3 The flowchart illustrates the recovery of Mn and Zn from dust collected by a baghouse dust collector after thermal desorption of soil.
[0043] Example 1 1. Ni, Fe, and some Cr are removed from the original ash using magnetic attraction to obtain magnetically adsorbed dust. The specific steps are as follows: After grinding the raw ash balls, pass them through a 150-mesh sieve and collect the portion that passes through the sieve. Two-stage electromagnetic separation is adopted, with the first stage having a magnetic induction intensity of 0.6T and the second stage having a magnetic induction intensity of 1.5T.
[0044] After magnetic adsorption, the removal rate of Ni in the original ash is ≥85%, the removal rate of Fe is ≥95%, and some Cr is removed; after magnetic adsorption, the content of heavy metals Fe and Ni in the dust is reduced to 300mg / kg and 47.66mg / kg, respectively.
[0045] 2. After magnetic attraction, the dust is washed with an alkaline solution of pH 13 to remove As and Cr; retain the solid material after alkaline washing and proceed to the next step. Specific steps are as follows: A 20.00 g sample of magnetically adsorbed dust was placed in a 250 mL polytetrafluoroethylene bottle. Three parallel samples were prepared with a liquid-to-solid ratio of 10:1 (mL:g). The sample was shaken at 30 rpm for 24 h on a rotary shaker. After shaking, the sample was centrifuged to obtain the supernatant and the solid after alkali washing. The supernatant was filtered through a 0.45 μm filter, and the concentrations of heavy metals (As, Cr, Mn, Pb, Zn) in the supernatant (leaching solution) were determined by ICP-MS (Agilent 7900, USA). The results are shown in Table 2 (the corresponding heavy metal concentrations in Table 2 are the average values of the corresponding heavy metal concentrations in the filtered solution).
[0046] Table 2. Heavy metal concentrations in leachate after filtration with membranes of different pore sizes (pH=13, unit: μg / L)
[0047] 3. Add acid to the alkali-washed solid to adjust the pH to 5.5. After the reaction, filter using a 0.45μm filter membrane to remove other metal ions and solid substances, obtaining a solution containing high concentrations of Mn and Zn, thus achieving the recovery of heavy metals Mn and Zn. The specific steps are as follows: Take 10.00 g of the alkali-washed solid sample and place it in a 250 mL polytetrafluoroethylene bottle. Set up 3 parallel samples with a liquid-to-solid ratio of 20:1 (mL:g). Shake at 30 rpm for 24 h on a rotary shaker. After shaking, centrifuge to obtain the supernatant. Filter the supernatant through 0.45 μm and determine the concentration of heavy metals (As, Cr, Mn, Pb, Zn) in the supernatant (acidic solution) using ICP-MS (Agilent 7900, USA). Taking full advantage of the significant difference in heavy metal solubility under weakly acidic pH conditions, the heavy metal concentrations in the solutions containing high concentrations of Mn and Zn are shown in Table 3 (the corresponding heavy metal concentrations in the table are the average values of the corresponding heavy metal concentrations in the filtered solutions).
[0048] Table 3. Heavy metal concentrations of the solids after alkali washing dissolved in acidic solution (pH=5.5, unit: μg / L)
[0049] 4. Recycle and reuse solutions containing high concentrations of Mn and Zn, and prepare Mn-Zn alloys using conventional metallurgical methods.
[0050] Example 2 The only difference from Example 1 is that the supernatant was filtered through a 0.22 μm filter in both steps 2 and 3; the results are shown in Tables 2 and 3.
[0051] Example 3 The only difference from Example 1 is that the supernatant was filtered at 100 kDa in both steps 2 and 3; the results are shown in Tables 2 and 3.
[0052] Example 4 The only difference from Example 1 is that the supernatant was filtered at 10 kDa in both steps 2 and 3; the results are shown in Tables 2 and 3.
[0053] Comparative Example 1 The only difference from Example 1 is that: magnetic attraction is not performed, and step 2 is performed directly. The concentration of heavy metals in the resulting leachate is shown in Table 4 below (Table 4 only lists As, Ni and Fe, and the corresponding heavy metal concentrations are the average values of the heavy metal concentrations in the filtered solution).
[0054] Table 4. Heavy metal concentrations in leachate after filtration with membranes of different pore sizes (pH=13, unit: μg / L)
[0055] It can be seen that the concentration of As ions in the leachate is low when Fe and Ni are present, indicating that the presence of Fe and Ni has a significant impact on the removal of As in step 2.
[0056] As can be seen from Examples 1-4, the acidic recovery liquid obtained by the recovery method of the present invention has high concentrations of Mn and Zn, while the concentrations of other heavy metals are low. When filtered using a 10 kDa filter membrane, the recovery rates of Mn and Zn reach 93.7% and 71.7%, respectively, realizing the resource utilization of dust after soil thermal desorption.
[0057] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.
Claims
1. A method for recovering Mn and Zn from dust of a bag filter after thermal desorption of soil, characterized in that, The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: The method comprises the following steps:
2. The method of recovering Mn and Zn according to claim 1, characterized by, The method comprises the following steps:
3. The method of recovering Mn and Zn according to claim 1 or 2, characterized by, The method comprises the following steps:
4. The method of recovering Mn and Zn according to claim 1, characterized by, The method comprises the following steps:
5. The method of recovering Mn and Zn according to claim 1 or 4, characterized by, The method comprises the following steps:
6. The method of recovering Mn and Zn according to claim 1, characterized by, The method comprises the following steps:
7. The method of recovering Mn and Zn according to claim 1, characterized by, The method comprises the following steps:
8. The method of recovering Mn and Zn according to claim 1 or 7, characterized by, The method comprises the following steps:
9. The method of recovering Mn and Zn according to claim 1, characterized by, The method comprises the following steps:
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